1. Field of the Invention
The present invention relates to an image forming device, and more specifically, relates to an image forming device that optically forms an image of the subject by a zoom lens system and outputs it as an electric signal by capturing the image by an image sensor, above all, an image forming device having a high-performance and small-size zoom lens system.
2. Description of the Related Art
In recent years, digital cameras with which images can be easily captured have been becoming widespread with the spread of personal computers. Accordingly, smaller-size digital cameras have been demanded, and it has been demanded that taking lens systems be smaller in size. On the other hand, since the number of pixels of image sensors tends to increase year by year, high optical performance corresponding to the increased number of pixels of the image sensors and ease of manufacture capable of handling the reduction in product cycle are required of taking lens systems. Moreover, since image magnification variation, particularly optical magnification variation with little image degradation is also required of general consumer digital cameras, various types of zoom lens systems have previously been proposed in order to meet the requirements for smaller size and higher performance, and an example thereof is disclosed in U.S. Patent Application Publication No. 2003/0138245.
However, in conventional zoom lens systems like that proposed in the above-mentioned patent application publication, it is difficult to simultaneously satisfy the conflicting requirements for smaller size, higher performance and ease of manufacture.